ABSTRACT Although, innate and adaptive immune functions are maintained in the oral mucosa during acute HIV/SIV infection, these responses become markedly impaired during chronic HIV infection and are not fully restored by combination anti-retroviral therapy (cART). Persistent oral mucosal inflammation/immune activation characterized by dysregulated proinflammatory cytokine production and oral dysbiosis are cardinal features of chronic HIV/SIV infection. Even though our understanding of oral mucosal dysfunction in HIV/SIV infection has improved, the underlying molecular mechanisms remain unknown and unexplored. Apart from cytokines and transcription factors, recent studies show microRNA (miRNA)-mediated gene regulation to be critical for immune cell differentiation, maturation, activation and inflammatory responses. Extensive studies in other chronic inflammatory diseases of the oral cavity (Periodontitis, Oral lichen planus. etc.) have revealed a causative role for miRNAs in disease pathogenesis resulting in their identification as promising therapeutic targets. However, the role of miRNAs in HIV induced oral mucosal dysfunction is lacking. This application builds on preliminary studies, which identified significant dysregulation of miRNAs linked to T and B-cell activation and epithelial barrier disruption in tonsils and buccal mucosa (BUCM) from chronically SIV-infected rhesus macaques. Studies of the same group using delta-9-tetrahydrocannabinol (??-THC) administration to chronic SIV-infected RMs significantly suppressed gastrointestinal proinflammatory gene/miRNA expression and inhibited T and B-cell activation and proliferation in vitro, suggesting their immense therapeutic potential for attenuating/reversing local (oral cavity) and systemic immune activation and slowing disease progression in the setting of suppressive cART. Based on our strong preliminary data demonstrating that miRNA expression is dysregulated in BUCM and tonsils in chronic HIV/SIV infection, we hypothesize that this leads to oral mucosal dysfunction, which contributes to immune activation and HIV disease progression. Further, we hypothesize that chronic ??-THC treatment may reduce inflammation, restore oral immune function, and slow HIV/SIV disease progression by modulating miRNA expression. A major goal of this application is to identify miRNA mechanisms associated with oral mucosal dysfunction and cannabinoid mediated suppression of immune activation. The project has three specific aims: 1) Test the hypothesis that miRNA (miR-142-3p,-142- 5p,-186,-7,-101-3p,-29b,-141) mediated downregulation of occludin (OCLN), claudin-1 (CLDN1) and zona occludens (ZO1) leads to oral epithelial barrier breakdown and increased epithelial permeability. 2) Identify miRNA mechanisms of cannabinoid-induced suppression of immune activation in BUCM and tonsils during the course of SIV infection. 3) Determine the effect of combination anti-retroviral treatment (cART) in conjunction with chronic ??-THC administration on the oral microflora, inflammation/immune activation, viral replication, miRNA expression and epithelial tight junction proteins in the oral cavity. The proposed research is novel and applies state of the art immunological and molecular approaches to address a significant gap in our understanding of the transcriptional and post-transcriptional mechanisms underlying oral mucosal dysfunction in the setting of suppressive cART. Additionally and more importantly, the results will deepen our understanding of the mechanisms underlying the anti-inflammatory effects of cannabinoids and have important therapeutic implications for targeted immune modulation in not only HIV but also other chronic inflammatory diseases of the oral cavity. Thus, the overall significance and impact is high.